Miki Yagita

Particulate formation and flame structure in diesel engines

This paper describes the particulate formation in diesel flames considering the flame structure and its similarity to that of gaseous turbulent diffusion flames. A comparison of spatial variations of soot concentration, equivalence ratio and flame temperature between diesel flames and turbulent diffusion flames reveals the facts that soot particles are mostly farmed in a region where the equivalence ratio is near stoichiometric and the flame temperature is the highest in both flames, and that in diesel flames this region exists generally near the flame tip. A close inspection of high speed photographs of diesel flames is discussed.

Flow around a Circular Cylinder with Ground Effect

The flow around a circular cylinder placed at various heights above a moving belt is investigated experimentally and numerically for the high Reynolds number (Re=7×104). The turbulent boundary layer on the belt is removed by moving belt and flow suction method. Furthermore, The calculations are performed by the boundary element method combined with the vortex method. The experimental results show that the presence of the belt affect remarkably the flow around the cylinder. The calculated results show that flow patterns and separation points agree qualitatively with the experimental ones.

Modification of k-.EPSILON. Model in Anisotropic In-Cylinder Flows.

The k-e model has been widely used to calculate turbulent flows in engine cylinder ; however, it has not been evaluated adequately whether the k-e model can be applied to anisotropic in-cylinder turbulent flows. In this paper, several modified k-e models and the algebraic stress equation model are evaluated for an anisotropic in-cylinder flow by a comparison of predicted velocity field with experimental result. Based on the comparison, a modified k-e model is newly proposed which can describe the mean and turbulent velocities of the flow in the pancake-shaped combustion chamber. The modified k-e model, however, still lacks the ability to reproduce turbulence in the combustion bowl in a piston.

LARGE-SCALE STRUCTURES IN THE WAKE BEHIND A CIRCULAR CYLINDER.

The authors have reported that the two-dimensional Karman vortices behind a cicular cylinder are broken into lengths of about 8d and form chains of spoon-shaped vortex couples. In the present experiment disks were attatched to the cylinder so that the Karman vortices were artificially cut at fixed positions with fixed lengths of 4d, 4d, 8d and 10d. The structures with 8d were most stable, forming the vortex chains with least irregularities, and the wake was much wider than that without the disks, while the neighbouring vortices with a length 4d were merged to the scale of about 8d. There results show that the length 8d is a unique scale in the deformation of the Karman vortices to the three-dimensional large-scale structure.